The present invention relates to an induction heating roller device, a heating roller for the induction heating roller, a fixing apparatus and an image forming apparatus.
A heating roller, which includes a thermal source composed of a halogen lamp, has heretofore been employed to thermally fix toner image onto record medium. Such a technology encounters an issue such as a prolonged warm-up time or an insufficient thermal capacity. To address this issue, considerable research and development work has been undertaken in the past to commercially apply an induction heating technology.
Japanese Patent Publication NO. 2000-215974 discloses an excitation coil located in close proximity to an object body to be heated for causing induction current to flow through the object body, with the excitation coil including a coil wire material wound in a plane and deformed in a shape to cope with a curved wall of the object body while a magnetic core is located in a position opposed to the object body with respect to both ends of the excitation coil in a longitudinal direction thereof such that the magnetic core cope with a curved surface of the excitation coil. (Related Art 1) Japanese Patent Publication NO. 2000-215971 discloses an induction heating device which includes a heating rotor body having an electromagnetic induction heating property, and a magnetic flux generating unit located inside the heating rotor body for generating magnetic flux of a high frequency to cause the heating rotor body to be heated up due to an electromagnetic induction heating for thereby heating the object body, with the magnetic flux generating unit including a core, made of magnetic material, and an electromagnetic transducer coil wound around the magnetic core, which is comprised of a core portion around which the electromagnetic transducer coil is wound, and a magnetic flux induction core portion opposed between distal ends portions in a magnetic flux gap for concentrating a magnetic flux at a portion of the heating rotor body more intensively than that concentrated at the core portion. (Related Art 2)
Any one of the Related Arts 1 and 2 employs a heating technology that uses an eddy-current loss which provides the same effect commercially realized in an IH cooker. A high frequency electric current to be utilized in such a heating technology is selected to have a frequency ranging from 20 to 100 kHz.
On the contrary, Japanese Patent Publication NO. 59-33787 discloses a high frequency induction heating roller which is comprised of a cylindrical roller body composed of electrically conductive material, a cylindrical bobbin located inside the cylindrical roller body in a concentric relationship, and an induction coil wound around an outer circumferential periphery of the bobbin in a spiral relationship to induce induction current in the roller body to compel it to be heated up. (Related Art 3)
With such a structure of the Related Art 3, the cylindrical roller body serves as a secondary coil of a closed circuit and the induction coil serves as a primary coil, with the primary and secondary coils being coupled in a transformer relationship to cause secondary voltage to be induced in the secondary coil of the cylindrical roller body. The presence of flow of secondary electric current through the closed circuit of the secondary coil responsive to the secondary voltage compels the cylindrical roller body to be heated up, i.e. in a so-called secondary side resistance heating technology. With this technology, the presence of stronger magnetic coupling than that achieved in the heating technology using the eddy-current loss increases a stationary efficiency while enabling the whole of the heating roller to be heated up, resulting in an advantage wherein a fixing device becomes more simple in structure than those of the Related Arts 1 and 2.
However, the Related Art 3 encounters an issue wherein a warm-up time can not be so shortened as expected. Upon considerable research and study conducted by the inventor, such an issue is deemed to originate from the resistance value of the secondary coil formed in the heating roller, which is not supervised.
In the Related Art 3, further, with the use of such a low frequency ranging from 20 to 100 kHz that is obtained in an IGBT inverter that is used in cooking equipments such as an induction heating type cooker or range, it is difficult for a high electric power transmitting efficiency to be obtained.